Continued development of novel fluorogenic enzyme substrates that yield intensely fluorescent precipitates near the site of enzymatic activity and their bioanalytical applications is proposed. Since the fluorescent precipitates represent pure dye, the substrates can be used to detect enzymatic activity with high spatial resolution. Work in phase I tested whether these substrates could be used for ultrasensitive detection in histochemistry, molecular biological techniques including DNA and RNA hybridization, detection of cell-surface receptors, and detection of enzymatic activity associated with living cells. Support is specifically requested for development of multi-color assays using these substrates and for synthesis of improved substrates for particular enzymes, resulting in greater solubility and cell permeability as well as wider choices of enzymes for enzyme-mediated detection. As these substrates represent an entire detection technology, rather than a tool for a single bioanalytical application, their market potential is broad, corresponding to that of chemiluminescent or colorimetric enzyme substrates, with the advantages of multi-color detection, compatibility with other fluorescent probes, fine structure localization, and signal stability.